This hokku is from the 12th month (January 1821).
The first plum blossoms have begun to appear, though the ground may be covered with snow. Presumably these plums have white blossoms that shine in the sunlight. In my own experience, January plum blossoms seem especially bright because most of the things around them are still a bit drab, and snow adds its own reflected light. If this were a first- or early 2nd-month hokku about plum blossoms falling and scattering, "fluttering" would be the image.
The word Issa uses for "head" (tsumuri) is rarely used by city people in 21st-century Japan, but in Issa's day it was common and referred to the head in a more bodily way than atama, which often has abstract connotations.

This hokku was found written in the margins Issa's travelog, Journey to Western Provinces (Saigoku kikou 西国紀行, 1795), when he was thirty-three. Locusts are an autumn word, and the travelog ends in early summer, so the hokku was probably written later than the travelog.

The onomatopoetic phrase bara-bara is typically used for the sound of large raindrops steadily hitting a roof and similar sounds of many objects lightly striking another object. The phrase implies that the hitting sounds are repeated, so Issa seems to have walked into a small, low-flying swarm of locusts, and some of them fly against his lower legs, hitting them again and again. He's probably wearing cotton leggings (kyahan), so the locusts make slapping or pattering sounds when they hit or graze his legs. Locusts usually do not attack or bite humans, so the collisions seem to be unintentional.

Translation and comment by Chris Drake

....................................

臑一本竹一本ぞ夕涼み
sune ippon take ippon zo yuusuzumi

just me
and a stalk of bamboo...
evening cool

Shinji Ogawa explains that sune ippon, literally "one shin," is akin to the English expression, "singlehandedly."
In the haiku, Issa is making his way in the world on his own: alone, except for his companion, the bamboo.

けふの日に降れ降れ皺の延薬kyoo no hi ni fure-fure shiwa no nobi kusurifall from the sky today!wrinkle-curingmedicine .On the fifth day of Fifth Month (Boy's Festival), rain water was captured and used to make medicine. In this haiku, Issa hopes for the unattainable.